The invention relates to a device for optically displaying thermal image scenes, comprising pneumatic infrared sensors, for example, temperature-sensitive gas cells.
It is known, for example, from German Offenlegungsschrift No. 2,534,586 (to which U.K. Pat. No. 1,557,029 corresponds) to pick up thermal image scenes by means of infrared (IR) sensors, followed by conversion of signals from these sensors into optical or electronic signals. The thermal scene is then scanned and, from the radiation picked up by the infrared sensor (sensors), an electrical signal voltage is produced. The electric signal voltage is used, for example, to actuate light emitting diodes or displays for optical display of the thermal image.
The known highly sensitive infrared sensors on the one hand require cooling to a temperature well below room temperature, while on the other hand thermal image forming devices comprising such sensors require complex deflection and scanning means.
From "Review of Scientific Instruments", Volume 20, Number 11, November 1949, pages 816-820, it is known to use a temperature-sensitive gas cell as a pneumatic infrared detector or sensor. Such a gas cell may be, for example, a Golay cell. Variations of the volume of a gas which is exposed to thermal radiation are then converted into mechanical, optically detectable variations of a mirror wherefrom a spectrum of the thermal radiation can be obtained.
For optically displaying of a thermal image scene, however, devices comprising infrared sensors in the form of this known gas cell are not suitable because the mirror construction required for the spectral analysis is much too complex for a thermal image forming device to achieve a nondisturbed display of thermal images and to maintain this display for a prolonged period of time.